Electrostatic charging apparatus



1965 J. R. BRADY ETAL 3,

ELECTROSTATIC CHARGING APPARATUS Filed May 27, 1960 Fig. 2 $23 JOSEPH R.BRADY R088? 7' G CUNNINGHAM IN V EN TORS ATTORNEYS United States Patent3,291,658 ELECTRGSTATIQ CHARGING APPARATUE' Joseph R. Brady and RobertG. Cunningham, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporationof New Jersey Filed May 27, 19%, Ser. No. 32,223 2 Claims. (Cl. 3l7262}This invention relates to the treatment of a moving web of material andmore particularly to a method of and apparatus for applying anelectrostatic charge to the surface of a moving web of non-conductingmaterial.

It is well known in the art to utilize corona discharge devices forapplying an electrostatic charge to web and sheet material. In practicean ionized zone is established between a grounded metal backplate andthe discharge devices, and the sheets to be charged are positioned inthe ionized zone for a short period of time. When a moving web ofmaterial is electrostatically charged as it passes through such a zonethe electrostatic attraction which occurs between the web and thebackplate causes the web to frequently contact the backplate, thusproducing an irregular friction drag on the moving web. It is quiteditficult, therefore, to maintain a uniform tension in the web or auniform feed thereof. With the method and apparatus of the presentinvention, these disadvantages of the known apparatus as regards to amoving web are avoided. Broadly, the present invention involves theestablishing of an ionized zone adjacent to the periphery of a groundedelectrically conducting roller, and moving the web through the ionizedzone in spaced relation to the periphery of the roller. Morespecifically the present invention contemplates the use of such a rolleras a guide for the web and as a grounded backplate for the coronadischarge device.

The primary object of the present invention is, therefore, to provide animproved apparatus for applying an electrostatic charge to the surfaceof a moving web of non-conducting material.

Another object of the present invention is to provide a novel method ofelectrostatically charging a moving web of nonconducting material.

Still another object ot the present invention is to provide an apparatusfor electrostatically charging a moving web of non-conducting materialwhich does no adversely aliect the uniformity of feed and tension in themoving web.

Yet another object of the present invention is to provide an apparatusfor electrostatically charging a moving web of non-conducting materialin which an ionized zone, through which the web is advanced to receivean electrostatic charge, is established adjacent to the periphery of agrounded electrically conducting roller over which the web is passed,thereby eliminating the need for a stationary backplate.

Still another object of the present invention is to provide a relativelysimple apparatus for and method of electrostatically charging a movingweb of non-conducting material which is efiicient and relativelyinexpensive to use.

Still other objects and advantages of the present invention will becomereadily apparent to those skilled in the art from the followingdescription with reference to the drawing in which like charactersdenote like parts and wherein:

FIG. 1 is a schematic view illustrating the preferred embodimelt of thepresent invention; and

FIG. 2 illustrates another embodiment of the present invention.

In FIG. 1 the character W designates a web of nonconducting material,such as, for example, paper, cardice board, plastic, etc., which isdrawn in the direction of the the arrow from a supply thereof (notshown) over the periphery of a grounded metal roller 11 by means of feedrollers 13 and i5. Electrically non-conductive feed rollers 13 and 15are driven in synchronism by means of an electric motor 17 and asuitable belt drive w. In order to facilitate the clarity of thedrawing, the mechanism by which the feed rollers 13 and 15 are connectedfor synchronous movement is not shown. Metal roller 11 is grounded asindicated at 21. A corona discharge device of the type well known in theart, with its projecting needle 23 is mounted in fixed relation in theapparatus with the needle extending preferably along a line whichintersects the rotational axis of roller 11. The tip of needle 23 isspaced from the periphery of roller 11 by a distance designated by thecharacter B. The web W after leaving the periphery of roller lll ispassed through a zone of ionized air which is maintained between theneedle 23 and ground when the corona discharge device is connected to asuitable unidirectional high voltage supply (not shown). This zone isschematically illustrated in the drawing by the dashed lines extendingbetween the periphery of the roller and the tip of needle 23. Whenpassing through the zone web W is spaced from the periphery of theroller ill by a distance designated by the character A. The dots placedadjacent to the surface of web W in the drawing are intended to indicatethe presence of electrostatic charges which have been deposited on theweb as a result of passing through the ionized zone.

Obviously the specific voltage which is required in any particularinstallation and the specific distances A and B which provide optimumcharging efficiency will vary depending upon the physical and electricalcharacteristics of the web which is to be charged and atmosphericconditions. We have found in one installation of apparatus of the typeillustrated in FIG. 1, that a DC. potential of approximately 3000 to12,000 volts applied between the needles and the grounded rollerresulted in a charge equiv alent to a web potential of approximately1560 to 19,000 volts as measured by an electrostatic field meter or heldmill as it is known in the art, to a paper web approxi mately 70 mm.wide and 0.075 mm. thick. In that installation the distance A wasapproximately 11 mm. and B approximately 37 mm. The resistivity of thepaper web was approximately 1x10 ohms-cm. Changing the spacing of theweb and corona discharge device so that A from 5 mm. to 25 and =frorn 8mm. to 5G does not decrease the eiliciency of the apparatus by more than20%. In the apparatus a corona discharge device having two spacedneedles was utilized in order to fully cover the 70 mm. width of thepaper, but if a different width web is to be charged the number ofneedles should be varied accordingly.

The fact that any grounded metal roller over which a non-conducting webnormally passes can function as a backplate during application of anelectrostatic charge to the moving web is unexpected, since it would bethought that any electrostatic charge picked up by the web would tend toleak oil to the grounded electrically conducting roller. This does notoccur, however, even with a relatively poor insulator such as paper. Itis possible to use such a roller as a contact backplate, as used incharging materials in sheet form, or as a backplate spaced at variousdistances from a moving web of material. In FIG. 2 the grounded metalroller 113i acts as a contact bacle plate for web W. The needle 123 ofthe corona discharge device is mounted opposite the arc of contact ofweb W with roller 111. In this instance the DC. potential between theneedle 12? and ground is kept between 30805000 volts. if greaterpotentials are utilized, discharges are .apt to occur between web W androllerrlll as the web is drawn away from the periphery of the roller.Again it should be realized that the exact potentials utilized may varyslightly depending upon the-material of web W. V I

It will now be appreciated by those skilled in the art that we havedisclosed a novel method and apparatus for electrostatically charging amoving web of non-conducting material. It is realized that manymodifications and varia tions of the embodiments specifically describedherein are possible. For example, it is also possible to place theneedles of the corona discharge device 25 mm. from the roller at thepoint of separation of the Web from the periphery of the roller andstill obtain satisfactory results. In that instance lower potentials forthe corona discharge device are required in order to provide the sameamount of electrostatic charge on the web as is obtained with thepreferred embodiment described herein. However, the ability to charge tovarious potential levels is lost. In view of this variation and theother modifications and variations which will become readily apparent tothose skilled in the art from theforegoing description, the descriptionis intended to be illustrative only and the scope in spaced relationwith respect to said grounded roller, said corona discharge device beingoperatively associated with said roller and being so located withrespect thereto as to maintain an ionized zone between said device and afirst portion of the periphery of said roller, means for moving said webabout said roller in surface contact with a second peripheral surfaceportion of said roller independent of said first surface portion and formoving said web between said roller and said corona discharge device,said second peripheral portion comprising all of the surface of theroller in contact with the web, whereby said web is passed through saidionized zone for deposition of an electrostatic charge thereon, andwhereby the relative spacings of said web and said corona dischargedevice from said roller may be varied to achieve optimum chargingefficiency. V V

2. Apparatus according toclaim 1 wherein said corona discharge device islocated such that said web is moved through said ionized zone afterleaving said second peripheral portion of said roller.

References Cited by the Examiner UNITED STATES PATENTS 1,854,071 4/32Schacht 317--3 2,681,036 6/54 Ewing et al. 317-262 2,711,481 6/55Phillips 3l7-3 2,935,418 5/60 Berthold et al 3l7--262 SAMUEL ,BERNSTEIN,Primary Examiner.

LLOYD YMCCOLLUM, Examiner.

1. IN AN APPARATUS FOR DEPOSITING AN ELECTROSTATIC CHARGE ON A WEB OFNONCONDUCTING MATERIAL, A ROLLER MOUNTED FOR ROTATION ABOUT AN AXIS FORGUIDING SAID WEB, SAID ROLLER BEING COMPRISED OF AN ELECTRICALLYCONDUCTIVE MATERIAL AND BEING ELECTRICALLY GROUNDED, A CORONA DISCHARGEDEVICE IN SPACED RELATION WITH RESPECT TO SAID GROUNDED ROLLER, SAIDCORONA DISCHARGE DEVICE BEING OPERATIVELY ASSOCATED WITH SAID ROLLER ANDBEING SO LOCATED WITH RESPECT THERETO AS TO MAINTAIN AN IONIZED ZONEBETWEEN SAID DEVICE AND A FIRST PORTION OF THE PERIPHERY OF SAID ROLLER,MEANS FOR MOVING SAID WEB ABOUT SAID ROLLER IN SURFACE CONTACT WITH ASECOND PERIPHERAL SURFACE PORTION OF SAID ROLLER INDEPENDENT OF SAIDFIRST SURFACE PORTION AND FOR MOVING SAID WEB BETWEEN SAID ROLLER ANDSAID CORONA DISCHARGE DEVICE, SAID SECOND PERIPHERAL PORTION COMPRISINGALL OF THE SURFACE OF THE ROLLER IN CONTACT IWITH THE WEB, WHEREBY SAIDWEB IS PASSED THROUGH SAID IONIZED ZONE FOR DEPOSITION OF ANELECTROSTATIC CHARGE THEREON, AND WHEREBY THE RELATIVE SPACINGS OF SAIDWEB AND SAID CORONA DISCHARGE DEVICE FROM SAID ROLLER MAY BE VARIED TOACHIEVE OPTIMUM CHARGING EFFICIENCY.